Optical disk apparatus

ABSTRACT

An optical disk apparatus for recording test data onto an optical disk while changing the level of recording power and determines the optimum recording power with reference to the quality of a reproduced signal of the test data. A modulation degree or a γ value is calculated from a reproduced signal of the test data, and the gradient of a change of the modulation degree or the γ value relative to the recording power Pw is calculated. Further, a target recording power is determined utilizing an area where the gradient of the change is relatively sharp, and the optimum recording power is determined based on the target recording power.

FIELD OF THE INVENTION

[0001] The present invention relates to an optical disk apparatus, andin particular to optimization of recording power for recording data ontoa recordable optical disk.

BACKGROUND OF THE INVENTION

[0002] OPC is known as a conventional technique for optimizing recordingpower. According to the OPC technique, test data is recorded onto anarea of an optical disk known as a Power Calibration Area, or PCA, whilechanging the level of the recording power. Specifically, a powerfunction (γ) is calculated using a reproduced RF signal relating to datafor test recording, and recording power at a level which results in thecalculated power function, or a γ value, having a predetermined targetvalue (a target recording power) is then calculated. Further, using thecalculated target recording power, the optimum recording power isdetermined. A γ value is defined as Expression 1, based on a modulationdegree m of a reproduced RF signal, and recording power Pw.

γ=(dm/dPw)/(m/Pw)  (1)

[0003] The right side (dm/dPw) of Expression 1 above is a value obtainedby differentiating a modulation degree m by recording power Pw.

[0004] In actuality, a target γ, a parameter ρ for use in calculation ofthe optimum recording power based on a target recording power, anerasing/recording power ratio ε, an erasing/recording power ratiocompensation coefficient for low speed recording κ, and so forth arerecorded in a read-in area on an optical disk, and read out for use indetermination of the optimum recording or erasing power.

[0005] That is, using a target recording power Pwt, which can produce atarget γ value, the following Expressions (2) to (4) are obtained.

Pwo=ρ·Pwt  (2)

Peo=ε·Pwo  (3)

Peo′=κPwo  (4)

[0006] In these expressions, Pwo is the optimum recording power, Peo isthe optimum erasing power for twice or four time speed, and Peo′ is theoptimum erasing power for a normal speed.

[0007] These values, including a target γ value, a parameter ρ, a powerratio ε, and so forth, as determined from an optical disk manufactureunder conditions of 25° C., a standard or slower speed, and a laserwavelength 785 nm, are recorded onto a manufactured optical disk.

[0008] However, because a modulation degree m for use in calculation ofa γ value contains an error due to variation of in-plane sensitivity ofa recording film of an optical disk, an error-contained γ value isgenerally resulted due to the error. This makes it difficult to uniquelydetermine a target recording power based on a target γ value designatedby an optical disk manufacturer, and also difficult to accuratelydetermine the optimum recording power.

[0009]FIG. 9 is a graph showing modulation degrees m relative torecording power at respective levels, and variation of a γ valuecalculated based on a modulation degree using Expression (1). Theabscissa of the graph corresponds to a recording power Pw for testrecording, while the left ordinate corresponds to a modulation degree mand the right ordinate corresponds to a γ value.

[0010] Because of an error contained in a modulation degree m,calculated γ values may fluctuate in the vicinity of a target γ value,which is here set, as an example, at 1.3, as shown in the drawing. Thatis, a unique level of recording power Pw which produces a target γ valuecan not readily be determined, if at all.

[0011] For example, in the example of FIG. 9, recording power levels P0,P1, P2, and P3 are candidates for the recording power level which canproduce a target γ value, or a γ target. As such, the obtained optimumrecording power will significantly vary depending on which one of thecandidates is chosen for the calculation. In other words, it isdifficult to determine the inherent optimum level in this method, whichmakes it difficult to maintain preferable recording quality (a wavejitter, an error rate, and so forth). Specifically, recording power at alevel significantly lower than the inherent optimum level may adverselyaffect jitter and error rate, while recording power at a levelsignificantly higher than the inherent optimum level may adverselyaffect reliability for repetitive recording.

SUMMARY OF THE INVENTION

[0012] The present invention aims to achieve accurate determination ofthe optimum recording power, even if a modulation degree m contains someerror.

[0013] According to one aspect of the present invention, there isprovided an optical disk apparatus, comprising means for recording testdata onto a predetermined area on the optical disk while changing alevel of recording power; means for reproducing the test data tocalculate a modulation degree for the recording power at each level; andmeans for setting an optimum recording power based on gradient of achange of the modulation degree relative to the recording power.

[0014] Specifically, the gradient of a change of a modulation degreerelative to recording power can be uniquely determined for each opticaldisk, even when the modulation degree contains some error. Therefore,use of the gradient of a change of a modulation degree relative torecording power allows unique determination of the optimum recordingpower.

[0015] In one embodiment of the present invention, recording power at alevel corresponding to a point of inflection at which the gradient of achange of a modulation degree relative to recording power alters may bedetermined as a target recording power, and the optimum recording powermay be determined based on the target recording power.

[0016] In another embodiment of the present invention, recording powerat a level which produces a modulation degree 0 is calculated throughextrapolation utilizing the gradient of a change of a modulation degreerelative to recording power in an area where the gradient is sharp, sothat the resultant recording power is determined as a target recordingpower, and the optimum recording power is determined using the recordingpower at the calculated level as the target recording power.

[0017] According to another aspect of the present invention, there isprovided an optical disk apparatus comprising means for recording testdata onto a predetermined area on the optical disk while changing alevel of recording power; means for reproducing the test data tocalculate a γ value for the recording power at each level; and means forsetting an optimum recording power based on gradient of a change of theγ value relative to the recording power.

[0018] Specifically, the gradient of a change of a γ value relative torecording power can be uniquely determined for each optical disk even ifthe γ value contains some error. Therefore, use of the gradient of achange of a γ value relative to recording power allows uniquedetermination of the optimum recording power.

[0019] The present invention is applicable to optical disk apparatusescapable of data recording, such as a CD-R drive, CD-RW drive, a DVD-Rdrive, a DVD-RW drive, and so forth.

[0020] The present invention will be more clearly understood withreference to the description of embodiments described below, but towhich the present invention is not limited.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The foregoing aspects and many of the attendant advantages ofthis invention will become more readily appreciated as the same becomebetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

[0022]FIG. 1 is a block diagram showing a structure of an optical diskapparatus according to the present invention;

[0023]FIG. 2 is a block diagram showing functions of a controller ofFIG. 1;

[0024]FIG. 3 is a flowchart of processing by the controller;

[0025]FIG. 4 is a graph showing a change of a modulation degree relativeto recording power;

[0026]FIG. 5 is a diagram explaining determination of the optimumrecording power based on the gradient of a change of a modulationdegree;

[0027]FIG. 6 is another diagram explaining determination of the optimumrecording power based on the gradient of a change of a modulationdegree;

[0028]FIG. 7 is a flowchart showing another processing by thecontroller;

[0029]FIG. 8 is a diagram explaining determination of the optimumrecording power based on the gradient of a change of a γ value; and

[0030]FIG. 9 is a graph showing correlation between recording power anda modulation degree and that between recording power and a γ value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] In the following, embodiments of the present invention will bedescribed based on the accompanying drawings.

[0032]FIG. 1 is a block diagram showing major elements of an opticaldisk apparatus according to a first embodiment of the present invention.

[0033] An optical disk 10 is subjected to CLV or CAV control by aspindle motor 12. Opposing-the optical disk 10 is an optical pick-up 14,which projects a recording power laser beam supplied from a laser diode(LD) toward the optical disk 10 to record data onto the optical disk 10.The optical pick-up 14 also projects a reproducing power laser beam,similarly supplied from the LD, toward the optical disk 10 to read outdata from the optical disk 10. With a data rewritable optical disk 10,an erasing power laser beam, supplied from the LD, is projected towardthe optical disk 10 to erase data recorded on the optical disk 10(reproducing power<erasing power<recording power). Methods for recordingdata recording onto an optical disk 10 may be divided into two types,one in which a recording power laser beam is projected toward theoptical disk 10 to fuse and sublime a recording film on the optical disk10 for formation of pits thereon, and another in which the recordingfilm in crystalline state is heated and then rapidly cooled forconversion into an amorphous state. Either method can be used inconjunction with this embodiment.

[0034] For data erasure, an erasing power laser beam is applied forrestoration of a crystal state from the amorphous state.

[0035] For data recording, recording data is encoded in an encoder 18,and supplied to an LD driver 16. The LD driver 16 creates a drivingsignal based on the encoded recording data, and supplies the resultantsignal to the LD in the optical pick-up 14 for data recording. Arecording power value to be set in the LD driver 16 is determinedaccording to a control signal from the controller 24. Specifically,prior to actual data recording, test data is recorded onto a PCA area onthe optical disk 10 while changing the recording power levels so thatthe optimum recording power can be determined based on the quality of asignal relating to the test data (OPC).

[0036] For data reproduction, the optical pick-up 14 supplies areproduced RF signal to an RF signal processor 20. The RF signalprocessor 20, which comprises an RF amplifier, an equalizer, abinarizer, a PLL section, and so forth, processes the received RF signalin these sections, and supplies the result to a decoder 22. The decoder22 decodes the received binarized RF signal based on a synchronous clockwhich is generated in the PLL section, and outputs the resultantreproduced data. The RF signal processor 20 supplies an amplified,reproduced RF signal also to a controller 24 for signal qualityevaluation.

[0037] It should be noted that other circuits which operate for datareproduction, such as a circuit for generating tracking and focus errorsignals for focus and tracking servo controls, a circuit for reproducinga wobble signal stored in the optical disk 10 for address demodulationor rotation control, and so on, are not described here because theseoperate similarly to a conventional drive.

[0038] Based on the evaluated quality of a reproduced signal relative tothe test data, the controller 24 determines the optimum recording power.Specifically, the controller 24 calculates a modulation degree m of areproduced RF signal supplied from the RF signal processor 20, anddetermines the optimum recording power based on the gradient of a changeof the modulation degree m relative to recording power, rather thancalculating a γ value. The controller 24 then supplies the determinedoptimum recording power to the LD driver 16.

[0039]FIG. 2 is a block diagram showing functions of the controller 24of FIG. 1. The controller 24, which is comprised by a microcomputer, hasa modulation degree calculation section, an OPC execution section, apower determination section, a memory, and a parameter memory. Themodulation degree calculation section, the OPC execution section, andthe power determination section can be realized using a single CPU,while the memory and the parameter memory can be realized using a RAM.

[0040] In the controller 24, a reproduced RF signal which. is suppliedfrom the RF signal processor 20 through an interface (not shown) issupplied to the modulation degree calculation section. The modulationdegree calculation section calculates, based on the reproduced RFsignal, a modulation degree m of a signal having a predeterminedfrequency, for example, a signal 11T among signals 3T to 11T. Data forthe calculated modulation degree m is stored in the memory correlatedwith data for the recording power PW at each level. The powerdetermination section determines a target recording power based on achange of the stored modulation degree m, and then determines theoptimum recording power based on the target recording power using aparameter recorded in the parameter memory.

[0041] In the following, the flow of processing will be described indetail with reference to FIG. 3, which is a flowchart of processing bythe controller 24.

[0042] Initially, the OPC execution section records test data onto a PCAarea on the optical disk 10 while changing the levels of recording powerPw (S101). The level of recording power Pw is variable over 14 stages,for example, and recording power at a different level is applied to eachsector in the PCA area in test data recording. After test datarecording, the modulation degree calculation section of the controller24 calculates a modulation degree m based on a signal 11T of thereproduced RF signal (S102). Specifically, the peak level Imax andbottom level Imin of a signal 11T are calculated to determine adifference between them, and a modulation degree m is calculated basedon the determined difference.

m=(Imax−Imin)/Imax

[0043] A value for each calculated modulation degree m is stored in thememory correlated to the recording power Pw at a corresponding level ofOPC (S103). For example, the memory may store recording power at levelsPw1, Pw2, and so forth, and corresponding modulation degrees m1, m2, andso forth, in the form of (Pw1, m1), (Pw2, m2), and so forth.

[0044] Thereafter, the power determination section calculates thegradient of a change of a modulation degree mi relative to recordingpower at a level Pwi (i=1 to 14) which is stored in the memory, and thendetermines a target recording power Pwt based on the calculated gradientof the change (S104). Further, the optimum recording power Pwo isdetermined based on the target recording power Pwt and a parameterstored in the parameter memory (S105).

[0045] In this embodiment, there are two methods for determining atarget power Pwt according to the gradient of a change of a modulationdegree relative to recording power. These methods will be described indetail in the following.

[0046] A Method Using a Point at Which Gradient Alters, or a Point ofInflection:

[0047]FIG. 4 is a graph showing change of a modulation degree mirelative to recording power at respective levels Pwi stored in a memoryin the controller 24. The abscissa of the graph corresponds to recordingpower Pw, while the ordinate corresponds to a modulation degree m.Generally, a modulation degree m increases for recording power Pw atlarger levels. The gradient of a change of a modulation degree m isrelatively sharp, substantially linear, in an area with recording powerPw at relatively low levels (Area P), while it is moderate in an areawith recording power Pw at relatively high levels (Area Q). That is,there is an area in which a modulation degree m increases largelyrelative to recording power Pw, in other words, the change in recordingpower Pw is smaller compared to a change of a modulation degree m.Focusing on this fact, the power determination section determines atarget recording power Pwt, utilizing an area where the gradient of achange of a modulation degree m relative to recording power Pw isrelatively sharp in comparison with a recording power Pw, in otherwords, a recording power Pw does not greatly change in comparison with amodulation degree m.

[0048]FIG. 5 shows a specific determination method. That is, because thegradient of a change of a modulation degree m relative to recordingpower Pw alters from being sharp in one area to being moderate inanother, there exists a point at which alteration occurs, referred to asa point of inflection. In FIG. 5, Point R corresponds to a point ofinflection of the modulation degree m relative to a recording power Pw.Extracting this point R, the power determination section determines therecording power at a level corresponding to the point R as a targetrecording power Pwt. Specifically, the power determination sectioncalculates the gradient of the change, which can be obtained as Δm/ΔPw,and extracts a point, as a point of inflection, at which the gradientalters by a predetermined value or greater. The power determinationsection then determines recording power at a level corresponding to thepoint of inflection as a target recording power Pwt. Should the point ofinflection be located between adjacent levels of recording power amongfourteen discrete levels, recording power at the level which is closestto the point of inflection may be determined as the target recordingpower.

[0049] Alternatively, recording power at a level which corresponds to apoint of inflection may be calculated through linear interpolation, tobe determined as a target recording power.

[0050] After determination of a target recording power Pwt, the powerdetermination section multiplies the target recording power Pwt byParameter z1, which is stored in the parameter memory, to determine theoptimum recording power Pwo. That is,

Pwo=z1·Pwt  (5)

[0051] Parameter z1 may be predetermined and stored in a read-in-area ofthe disk by an optical disk manufactures, and the optical pick-up 14reads it out and stores it in the parameter memory. Alternatively, aparameter may be stored in a memory in a driver, or in a parametermemory, during the process of manufacturing the drive.

[0052] Because a point of inflection, or a point at which the gradientof a change alters, can be uniquely determined even if the absolutevalue of a modulation degree m fluctuates due to an error contained inthe modulation degree m, a unique target recording power Pwt can bedetermined. This in turn makes it possible to determine a unique valuefor the optimum recording power using Expression 5 based on a targetrecording power Pwt. Therefore, according to this method, a target γvalue is unnecessary, and parameter z1 is used in the place of parameterρ.

[0053] A Method Using Extrapolation of the Gradient of a Change of aModulation Degree m:

[0054]FIG. 6 shows another method for determining the optimum recordingpower. The drawing shows, similar to FIG. 4, a change of a modulationdegree m relative to recording power Pw at respective levels.Specifically, any two points are extracted from a range with thegradient of the change being substantially linear within Area P with thegradient being sharp, and connected by a straight line L, which is thenextended. With this extension, recording power at a level correspondingto the modulation degree m being 0 is obtained.

[0055] It should be noted that Area P can be extracted by calculatingthe gradient of the change Δm/ΔPw and selecting an area in which theabsolute value of the gradient exceeds a predetermined value. It shouldalso be noted that whether or not the gradient is substantially linearcan be determined based on whether or not the absolute value of adifference between the gradients of two adjacent changes, Δm/ΔPw, issmaller than a predetermined differential value.

[0056] While using the recording power at a level corresponding to amodulation degree m being 0 as a target recording power Pwt, the targetrecording power Pwt is multiplied by parameter z2, which is stored inthe parameter memory, to determine the optimum recording power Pwo.

[0057] That is,

Pwo=z2·Pwt  (6)

[0058] Parameter z2 can be predetermined and stored in a read-in-area ofthe disk by an optical disk manufactures. The value is read using theoptical pick-up 14 and stored in the parameter memory.

[0059] Because the gradient of a change of a modulation degree mrelative to recording power can be uniquely determined even if theabsolute value of a modulation degree m fluctuates due to an errorcontained in the modulation degree m, a unique target recording powerPwt can be determined. This in turn makes it possible to determine aunique value for the optimum recording power, using Expression 6 basedon target recording power Pwt. That is, according to this method, atarget γ value is unnecessary, and parameter z2 is used in the place ofparameter ρ.

[0060] It should be noted that, whereas any two points are extractedfrom an area with the gradient of the change being sharp andsubstantially linear and connected to each other to thereby create astraight line in this example, extraction of points is not limited tothe example described. For example, three or more points may beextracted and connected to one another to thereby create a straight linefor calculation of recording power at a level which corresponds to amodulation degree m being 0.

[0061] It should be noted that, whereas a modulation degree m of testdata is calculated and a target recording power, and then the optimumrecording power, are calculated based on the gradient of a change of themodulation degree relative to recording power in the above embodiment, aγ value may be calculated based on the modulation degree m so that theoptimum recording power can be determined based on the gradient of achange of the γ value.

[0062] In the manner of determination of a target recording power basedon the absolute value of a γ value (recording power at a level whichachieves a target γ value, is determined as a target recording power),it is difficult to uniquely determine a target recording power shouldthe γ value fluctuate due to an error. This in turn makes it difficultto accurately determine the optimum recording power. However, thisproblems can be addressed when the gradient of a change of a γ value isbased on in determination of a target recording power.

[0063]FIG. 7 shows a flowchart of another processing by the controller24. This process flow differs from that of FIG. 3 in that the powerdetermination section calculates a γ value based on a modulation degreem (S202), and that a target recording power Pwt is determined based onthe gradient of a change of the γ value relative to recording power Pw(S204).

[0064]FIG. 8 shows a method for determining the optimum recording power.The abscissas of the drawing corresponding to recording power Pw, whilethe left ordinate corresponds to a modulation degree m and the rightordinate corresponds to a γ value.

[0065] As shown, while focusing on Area S with the gradient of a changeof a γ value being sharp, two points are extracted from a range with thegradient being substantially linear and connected to thereby create astraight line, and recording power at a level Pw which achieves a γvalue being 0 is calculated based on the straight line. It should benoted that Area S can be determined by selecting an area where theabsolute value of the gradient of a change of a γ value, Δγ/ΔPw, exceedsa predetermined value, and that whether or not the gradient changessubstantially linearly can be determined based on whether or not theabsolute value of a difference between gradients of adjacent changes,Δγ/ΔPw, is smaller than a predetermined differential value.

[0066] While using the calculated recording power as a target recordingpower Pwt, the target recording power Pwt is multiplied by pre-storedparameter z3 to determine the optimum recording power Pwt.

Pwo=z3·Pwt  (7)

[0067] Parameter z3 also can be predetermined and stored in aread-in-area of the disk by the manufacturer, and the optical pick-up 14can reads out and store data for this parameter in the parameter memory.

[0068] Because the target recording power Pwt can be uniquely determinedbased on the gradient of a γ value even if the γ value fluctuates due toan error attributed to an error in a modulation degree m, the optimumrecording power Pwo can be accurately determined.

[0069] As described above, because the optimum recording power isdetermined based not on the absolute value of a γ value but on thegradient of a change of a modulation degree m or of a γ value in thisembodiment, accurate determination free from the influence of either anerror in the modulation degree m or fluctuation of its absolute value isachievable. This improves recording quality.

[0070] After determination of the optimized recording power, the optimumerasing power can be determined using Expressions 3 and 4 and Parameterε.

[0071] It should be noted that, whereas a recording power is optimizedusing the gradient of a change in the above embodiment, an erasing powermay be optimized in a similar manner. Specifically, a target recordingpower is calculated using the method described above, and the optimumerasing power Peo is then determined using parameter z1e and thefollowing Expression:

Peo=z1e·Pwt  (8)

[0072] wherein z1e is a parameter corresponding to z1, and generallyz1e<z1.

[0073] In this embodiment, a target recording power is determined basedon a change of a modulation degree m relative to a recording power Pw,that is, Δm/ΔPw. However, it is obvious to a person skilled in the artthat, when a recording power Pw is changed by a constant level, a targetrecording power can also be determined with calculation of Am aloneaccording to the OPC technique. For example, for recording powershifting by 0.5 mW, such as 6 mW, 6.5 mW, 7 mW, 7.5 mW, and so forth, apoint of inflection (see FIG. 5) and an extrapolation point (see FIG. 6)can be determined using solely a change Am of a modulation degree m. Inthese cases also, a target recording power is determined basedsubstantially on a change of a modulation degree relative to recordingpower.

[0074] In this embodiment, a target recording power is determined andthen multiplied by a coefficient to determine the optimum recordingpower, and further erasing power. Erasing power, which can be determinedbased on the optimum recording power, can also be calculated baseddirectly on the target recording power through multiplication using acoefficient. Alternatively, a target recording power may be multipliedby a coefficient to determine the optimum erasing power, which is thenmultiplied by another coefficient to determine the optimum recordingpower.

[0075] While the preferred embodiments of the invention have beenillustrated and described, it will be appreciated that various changescan be made therein without departing from the spirit and scope of theinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. An optical diskapparatus, comprising: means for recording test data onto apredetermined area on an optical disk while changing a recording powerlevel; means for reproducing the test data to calculate a modulationdegree for the recording power at each level; and means for setting anoptimum recording power based on gradient of a change of the modulationdegree relative to the recording power.
 2. The optical disk apparatusaccording to claim 1, wherein the means for setting an optimum recordingpower sets the optimum recording power based on the recording power at apoint at which the gradient of a change of the modulation degreerelative to the recording power alters.
 3. The optical disk apparatusaccording to claim 1, wherein the means for setting an optimum recordingpower sets the optimum recording power by multiplying the recordingpower at a point at which the gradient of a change of the modulationdegree relative to the recording power alters by a coefficient.
 4. Theoptical disk apparatus according to claim 1, wherein the means forsetting an optimum recording power sets the optimum recording powerutilizing an area where the gradient of a change of the modulationdegree relative to the recording power is relatively sharp.
 5. Theoptical disk apparatus according to claim 4, wherein the means forsetting an optimum recording power sets the optimum recording powerbased on a recording power for which the modulation degree is zero whencalculated based on the gradient in the area.
 6. The optical diskapparatus according to claim 4, wherein the means for setting an optimumrecording power sets the optimum recording power by multiplying acoefficient and a recording power for which the modulation degree iszero when calculated based on the gradient in the area.
 7. The opticaldisk apparatus according to claim 1, wherein the means for setting anoptimum recording power further sets an optimum erasing power based on agradient of a change of the modulation degree relative to the recordingpower.
 8. An optical disk apparatus, comprising: an optical pick-up forirradiating a laser beam onto an optical disk to record or reproducedata; a signal processing circuit for detecting a modulation degree froma reproduced signal supplied from the optical pick-up; and a controllerfor setting an optimum recording power based on the modulation degree toadjust laser beam power of the optical pick-up, wherein the opticalpick-up records and reproduces test data with respect to the opticaldisk, using laser beam power at a plurality of levels, the signalprocessing circuit detects a modulation degree with respect to laserbeam power at each level, and the controller sets a target recordingpower based on gradient of a change of the modulation degree relative tothe laser beam power, and further sets the optimum recording power basedon the target recording power.
 9. The optical disk apparatus accordingto claim 8, wherein the controller sets the target recording power basedon a point of inflection at which the gradient of a change of themodulation degree relative to the laser beam alters.
 10. The opticaldisk apparatus according to claim 8, wherein the controller sets atarget recording power for which the modulation degree is zero, throughextrapolation using the gradient of change in an area where the gradientis sharp.
 11. The optical disk apparatus according to claim 8, furthercomprising: a memory for storing a parameter, wherein the controllersets the optimum recording power by multiplying the target recordingpower by the parameter stored in the memory.
 12. An optical diskapparatus, comprising: means for recording test data onto apredetermined area on an optical disk while changing a level ofrecording power; means for reproducing the test data to calculate a γvalue for the recording power at each level; and means for setting anoptimum recording power based on gradient of a change of the γ valuerelative to the recording power.
 13. The optical disk apparatusaccording to claim 12, wherein the means for setting an optimumrecording power sets the optimum recording power utilizing an area wherethe gradient of a change of the γ value relative to the recording poweris relatively sharp.
 14. The optical disk apparatus according to claim13, wherein the means for setting an optimum recording power sets theoptimum recording power based on a recording power for which the γvalue, calculated based on the gradient in the area, is zero.
 15. Theoptical disk apparatus according to claim 13, wherein the means forsetting an optimum recording power sets the optimum recording power bymultiplying a coefficient and a recording power for which the γ value,calculated based on the gradient in the area, is zero.
 16. The opticaldisk apparatus according to claim 12, wherein the means for setting anoptimum recording power further sets an optimum erasing power based onthe gradient of a change of the γ value relative to the recording power.17. An optical disk apparatus, comprising: an optical pick-up forirradiating a laser beam to an optical disk to record or reproduce data;a signal processing circuit for detecting a γ value from a reproducedsignal supplied from the optical pick-up; and a controller for settingan optimum recording power based on the γ value to adjust laser beampower of the optical pick-up, wherein the optical pick-up records andreproduces test data with respect to the optical disk, using laser beamsat a plurality of power levels, the signal processing circuit detects aγ value with respect to laser beam power at each level, and thecontroller sets a target recording power based on gradient of a changeof the γ value relative to the laser beam power, and further sets theoptimum recording power based on the target recording power.
 18. Theoptical disk apparatus according to claim 17, wherein the controllersets a target recording power for which the γ value is zero, throughextrapolation using the gradient of the change in an area where thegradient is sharp.
 19. The optical disk apparatus according to claim 17,further comprises: a memory for storing a parameter, wherein thecontroller sets the optimum recording power by multiplying the targetrecording power by the parameter stored in the memory.